

Confusingly, the explanations used two adjectives: "equivalent" and "identical".
Text should say: "A variable is only equivalent to a sharing variable".
Examples:
X==Y : false
X=Y, X==Y : true
X=A, Y=A, X==Y : true
A=B, X=A, Y=B, X==Y : true
A=f(X)
, B=f(X)
, A==B : true
A=f(X)
, B=f(Y)
, A==B : false
A=f(X)
, B=f(Y)
, X=Y, A==B : true
A=f(X)
, B=A, A==B : true