# Tell Mathematica to use symbolic expression

I would like to achieve a function sin as in:

T=Sin[t];
sin[x_]:=T/.t->x;


But without this replacement rule. How can I tell Mathematica plug in the definition of the variable first before defining the function?

I want Mathematica to treat T exactly as if I used Sin[t]. How can I achieve that?

• T[t_] = Sin[t]; then T[x] evaluates to Sin[x] – Bob Hanlon Nov 20 '17 at 17:57
• I want to use T as if i copy pasted the expression T stands for. I dont want T to be another function – Mr Puh Nov 20 '17 at 18:06
• Use T = Sin[t]; sin[t_] = T; then sin[x]  evaluates to Sin[x]  – Bob Hanlon Nov 20 '17 at 18:13
• I want to use T also in environments like sin=Function[t,T] – Mr Puh Nov 20 '17 at 18:25
• Since Function has the attribute HoldAll you would need to use sin = Function[t, Evaluate@T] – Bob Hanlon Nov 20 '17 at 18:29