Question: The for loop does not recognize alias

In using maple 17, for a for loop, the alias command is valid outside the for loop, but entering the for loop, maple verifies that alias is not recognized.The code is as follows:
with(PDEtools):
for k from 1 to 4 do
alias(u[k]=u[k](x,y,t));
alias(a[k]=a[k](x,y,t));
od:
print(has(a[1],x));
sol:=[]:
for i from 1 to 4 do
sol:=[sol[],a[i]=rhs(isolate(a[i]+diff(a[i],x)+i=0,diff(a[i],x)))];
print(has(a[i],x));
end do;
The output is as follows: thequestionofalias
true
[a[1] = a[1] + 1]
false
[a[1] = a[1] + 1, a[2] = a[2] + 2]
false
[a[1] = a[1] + 1, a[2] = a[2] + 2, a[3] = a[3] + 3]
false
[a[1] = a[1] + 1, a[2] = a[2] + 2, a[3] = a[3] + 3, a[4] = a[4] + 4]
false
Why is it outside the loop? A [1] ... A [4] has the variable x, but either a [ I ] or a [1] has no variable X.Send the question to the Forum and see which expert can answer it. See how you can make the alias command work inside a for loop! I'd appreciate it if you could answer that!