10 REM Boy's Surface
20 REM From the book "Topologicon" by Jean-Pierre Petit
100 PI=3.141592:P3=PI/3:P6=PI/6:P8=PI/8
110 HGR : POKE 49234,0
120 HCOLOR=3
130 FOR MU = 0 TO PI STEP 0.1
140 D=34+4.79*SIN(6*MU-P)
150 E=6.73*SIN(3*MU-P6)
160 A=D+E
170 B=D-E
180 AL=(P8)*SIN(3*MU)
190 C1=A*A-B*B
200 C2=SQR(A*A+B*B)
210 CM=COS(MU)
220 SM=SIN(MU)
230 FOR TE=0 TO 6.282 STEP .03
240 X1=C1/C2+A*COS(TE)-B*SIN(TE)
250 Z1=C2+A*COS(TE)+B*SIN(TE)
260 REM KOORDINATEN
270 X=X1*CM-Z1*SIN(AL)*SM
280 Y=X1*SM+Z1*SIN(AL)*SM
300 REM ZEICHNUNG
310 HPLOT 140+X,96+Y
320 NEXT TE
330 NEXT MU