ItIsSquare Definition

# Are the Points Q,T,S,R vertices of a square?

ItIsSquare:=proc(Q,T,S,R):

ItIsZero ( DeSq (Q,T) - DeSq (T,S)) and
ItIsZero ( DeSq (Q,T) - DeSq (Q,R)) and
ItIsZero ( DeSq (Q,T) - DeSq (R,S)) and
ItIsZero (Slope (Q,R)*Slope (Q,T) + 1) :

end:

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