I have a very simple task:

convert([a,b],`*`)

the result is of course a*b.  However if I load the Physics package beforehand, that is,

with(Physics)
convert([a,b],`*`)

the followinkg error shows up:

Error, unrecognized conversion: Physics:-`*`

I have read that the Physcs package redefines the mutiplication. This must be the source of the problem.
But how can I proceed. I need to do this task with the Physics package loaded. 
Any help will be appreciated! 

I need to sustitute many similar expressions. 
Somthing like:

subs( {f(x1)=h(x1), f(x2)=h(x2)...., f(xn)=h(xn)}, expression)

How can I ask Maple to substitute 

f(anything) = h(same thing)? 

(In Mathematica this can be done with x_) 

Even more general, how can I substitute, for example, 

F(f(x)) = H(h(x))
where f(x) is really 'anything'? 

Thanks! Max

I have found an unpleaseant feature of the define command. 
@Carl Love
See below for the example. Basically, after declaring a function orderless via the define command, 
a simple use of Categorize stops working.  Details in the file. 

How can one define a function f(x,y) to be symmetric under interchange x<-> y

 primes2.mw

primes.mw

As a result of a calculation I have a long expression. I give it a name, say, X,

X:= long expression. 

I try to use typematch to extract different parts of X and its does not work (it returns false).  

If, however, I copy and paste the long expression from the output and plug into my typematch query it works!   

It seems that copy and paste change the type of the expression. I am very confused with this. 

I have uploaded a file with the problem at the beggining.  Thank you! 
Max