Butterfly:=proc() local P,t,i,R,L,M,X,Y,O:
for i from 1 to 4 do
P[i]:=
ParamCircle
( O,R,t[i] )
od:
M:=Pt
( Le(P[1],P[3]) ,
Le
(P[2],P[4]) ):
L:=PerpPQ(O,M):
X:=Pt
(
Le(P[1],P[4]) , L):
Y:=Pt
(
Le(P[2],P[3]) , L ):
ItIsZero( DeSq(M,X)
- DeSq(M,Y) ):
end: