def functions on advanced graphing

[compsystems]

but on CAS V1:="X*Y=2" returns (X,Y)->false

same for

V1:=' X-2*Y=7' returns (X,Y)->false
V2:=' 5*X-3*Y=2'

Advanced_Graphing.V1(X,Y):= X-2*Y=7;
returns (X,Y)->false (CAS)
Error: Invalid input (Home)
Advanced_Graphing.V2(X,Y):= 5*X-3*Y=2;

CAS("V1(X,Y):=X-2*Y=7") returns program([0.,0.],[0.],false)
CAS("V2(X,Y):= 5*X-3*Y=2")

and how do I eliminate them then the variables V1, V2
purge(Advanced_Graphing.V2); // not work

HOME
purge(X,Y);
Advanced_Graphing.V1(X,Y):= 'X-2*Y=7' => Error: Invalid input
Advanced_Graphing.V1:='X-2*Y=7' // ok

purge(X,Y);
Advanced_Graphing.V2(X,Y):= '5*X-3*Y=2';
Advanced_Graphing.V2:= '5*X-3*Y=2'; // ok