Question: how to control the timing of evaluation

Hello people in mapleprimes,

I wonder if there is not any way to control the timing of substitution.

For  example,

x:=(t^(1-s)+s^(1-2*s))^a;mu:=c^(a-b)/'x';

brings mu := c^(a-b)/x. Please note that I made x unevaluated with '' around x, so that,

into the output of mu, the definition of x of (t^(1-s)+s^(1-2*s))^a does not appear.

But, in this case, when I typed the expression of

1+mu

and clicked return, the definition of x is inserted into the result of 1+m, though

I want x to remain x yet.

Surely, if I wrote ''x'' in stead of 'x', 1+mu does not contain the definition of x.

But, in that case as well, when I have other following calculations, in those the definition 

of x should apear, which I don't like.

On the other hand, when I write as

x:=(t^(1-s)+s^(1-2*s))^a; x:='x';
mu:=c^(a-b)/x; 1+m;

surely as x is initialized once, the result of mu and 1+mu does not cotain the definition of x.

But, in this case, I have to write x:=(t^(1-s)+s^(1-2*s))^a; when I want the definition of x

to be inserted. Though in this case the definition of x is short, original relations I have and

haven't writen above is a little more complicated, so that to insert is not desiable.

Aren't there any good way to evaluate the value of particular variables and to leave them

unevaluated at each time I want to choose each one?

I hope I could have written my question as easly understood.

And, thanks in advance.

taro