How to make Matlab recognize that an expression rewritten by using subexpr() is equal to the original expression?

I would expect the isAlways() function below to return 1 but for some reason Matlab does not recognize that x=x_2. Is there a way to solve this problem?

syms a b c d e f x
x = a + (a+b+c+d+e)^(1/2) + c*(e+f+(a+b+c+d+e)^(1/2));
x_2 = subexpr(x)

 
sigma = 
 

x_2 = 

isAlways(x_2==x)

Warning: Unable to prove 'a + sigma + c*(e + f + sigma) == a + c*(e + f + (a + b + c + d + e)^(1/2)) + (a + b + c + d + e)^(1/2)'.

ans = logical
   0

Answer 1

[Torsten]

You have to resubstitute sigma by (a+b+c+d+e)^(1/2) in x_2 to compare with x:

syms a b c d e f x
x = a + (a+b+c+d+e)^(1/2) + c*(e+f+(a+b+c+d+e)^(1/2));
x_2 = subexpr(x)

 
sigma = 
 

x_2 = 

isAlways(subs(x_2)==x)

ans = logical
   1