mirror of
https://github.com/michaelcmartin/Ophis.git
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219 lines
3.4 KiB
HTML
219 lines
3.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<HTML
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><HEAD
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><TITLE
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>Example: Fibonnacci Numbers</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
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REL="HOME"
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TITLE="Programming with Ophis"
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HREF="book1.html"><LINK
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REL="UP"
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TITLE="Call Stacks"
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HREF="c900.html"><LINK
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REL="PREVIOUS"
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TITLE="Our Goals"
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HREF="x915.html"><LINK
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REL="NEXT"
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TITLE="Example Programs"
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HREF="a975.html"></HEAD
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><BODY
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CLASS="SECTION"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Programming with Ophis</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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ACCESSKEY="P"
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><<< Previous</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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>Call Stacks</TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="a975.html"
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>Next >>></A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECTION"
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><H1
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CLASS="SECTION"
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><A
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NAME="AEN967"
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>Example: Fibonnacci Numbers</A
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></H1
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><P
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> About the simplest <SPAN
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CLASS="QUOTE"
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>"interesting"</SPAN
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> recursive function
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is the Fibonacci numbers. The function fib(x) is defined as being
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1 if x is 0 or 1, and being fib(x-2)+fib(x-1) otherwise.
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</P
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><P
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> Actually expressing it like that directly produces a very
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inefficient implementation, but it's a simple demonstration of the
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system. Here's code for expressing the fib function:
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</P
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><TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="PROGRAMLISTING"
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>.scope
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; Uint16 fib (Uint8 x): compute Xth fibonnaci number.
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; fib(0) = fib(1) = 1.
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; Stack usage: 3.
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fib: lda #$03
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jsr save'stack
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lda fun'vars
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cmp #$02
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bcc _base
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dec fun'args
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jsr fib
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lda fun'args
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sta fun'vars+1
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lda fun'args+1
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sta fun'vars+2
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lda fun'vars
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sec
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sbc #$02
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sta fun'args
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jsr fib
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clc
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lda fun'args
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adc fun'vars+1
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sta fun'args
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lda fun'args+1
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adc fun'vars+2
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sta fun'args+1
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jmp _done
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_base: ldy #$01
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sty fun'args
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dey
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sty fun'args+1
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_done: lda #$03
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jsr restore'stack
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rts
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.scend</PRE
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></TD
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></TR
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></TABLE
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><P
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> The full application, which deals with interfacing with CBM BASIC
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and handles console I/O and such, is in <A
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HREF="x1030.html"
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><I
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><I
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>fibonacci.oph</I
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></I
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></A
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>.
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</P
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="x915.html"
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ACCESSKEY="P"
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><<< Previous</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="book1.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="a975.html"
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ACCESSKEY="N"
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>Next >>></A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Our Goals</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="c900.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>Example Programs</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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> |