00100	BEGIN "TEST10"
00200		REQUIRE "ABBREV[SYS,BGB]" SOURCE_FILE;
00300		REQUIRE "SAITRG[SYS,BGB]" SOURCE_FILE;
00400		REQUIRE "DPYIII[SYS,BGB]" SOURCE_FILE;
00500	
00600		REAL X1,Y1,Z1;
00700		REAL X2,Y2,Z2;
00800		REAL X3,Y3,Z3;
00900		REAL X4,Y4,Z4;
01000		REAL X5,Y5,Z5;
01100		REAL R1,R2,R3,R4,R5;
01200		REAL A,B,T,C,S;
01300	
01400		SAFE INTEGER ARRAY DPYBUF[0:600];
01500	
01600		X1←X3←500;
01700	
01800	WHILE TRUE DO
01900	BEGIN
02000		DPYSET(DPYBUF);
02100		AIVECT(X1,Y1);
02200		AVECT(X2,Y2);
02300		AVECT(X3,Y3);
02400		AIVECT(200,200);
02500	
02600		R1 ← SQRT (X1*X1 + Y1*Y1 + Z1*Z1);
02700		R3 ← SQRT (X3*X3 + Y3*Y3 + Z3*Z3);
02800	
02900		C  ← (X1*X3 + Y1*Y3 + Z1*Z3)/(R1*R3);
03000	
03100	α CROSS V1 INTO V3 YIELDS  V4;
03200		X4 ← (Y1*Z3 - Y3*Z1);
03300		Y4 ← (X3*Z1 - X1*Z3);
03400		Z4 ← (X1*Y3 - X3*Y1);
     

00100	α CHEAP PLANE COEFFICIENTS;
00200		T ← X1*Y3 - X3*Y1;
00300		A ← (Z3*Y1 - Z1*Y3)/T;
00400		B ← (X3*Z1 - X1*Z3)/T;
00500	
00600	α IS THE CROSS'ED POINT V4 ABOVE OR BELOW THE CCW PLANE ? ;
00700		S ← (A*X4 + B*Y4 + Z4);
     

00100		DPYSST(CVS(ATAN2(Y3,X3)*1800/(π*10))&"   ");
00200		DPYSST(CVS((IF S<0 THEN -1 ELSE 1)*ACOS(C)*1800/(π*10)));
00250		AIVECT(200,100);DPYSST(CVG(S));
00300		DPYOUT(1);
00400		X3 ← X3 - 0.01*Y3;
00500		Y3 ← Y3 + 0.01*X3;
00600	END;
00700	
00800	END "TEST10";