ItIsParallelogram Definition

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

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

ItIsZero( Slope(Q,T)   -   Slope(S,R))   and   ItIsZero( Slope(T,S)   -   Slope(R,Q))  :

end: