set o = {} ;
reconsider y1 = {{}} as set ;
reconsider y2 = {{}} as set ;
reconsider y3 = {} :-> {} as Function of y2,y1 ;
reconsider y4 = {} :-> {} as Function of y2,y1 ;
reconsider y5 = ({},{}) :-> {} as Function of [:y2,y2:],y2 ;
reconsider x = [y1,y2,y3,y3,y5] as quintuple set ;
take x ; :: thesis: x is StrCategory-like
thus x is StrCategory-like ; :: thesis: verum