 
 
 
An operator is an infixed function : for example ’+’ is an 
operator and ’sin’ is a function.
An expression can be represented by a tree. The top of the tree is 
either an operator, or a function and the leaves of the tree are the 
arguments of the operator or of the function 
(see also 5.40.11).
The instruction sommet (resp. feuille (or op))
returns the top (resp. the list of the leaves) of an expression.
Input :
Output :
Input :
Output :
Input :
or :
Output :
Input :
or :
Output :
 
Remark
Suppose that a function is defined by a program, for example 
let us define the pgcd function :
Then input :
Output :
Then input :
Output :
Then input :
Output :
Then input :
Output :
 
 
