### 5.14.3 Define an operator: user_operator

user_operator takes as argument :

- a string : the name of the operator,
- a function of two variables with values in ℝ or in true, false,
- an option Binary for the definition or Delete to delete this definition.

user_operator returns 1 if the definition is done and else returns 0.

Example 1
Let R be defined on ℝ by x R y= x*y+x+y.
To define the law R, input :

user_operator("R",(x,y)->x*y+x+y,Binary)

Output :

1

Input :

5 R 7

Do not forget to put spaces around R.
Output :

47

Example 2
Let S be defined on ℕ by :
for x and y integers, x S y <=> x and y are not coprime.
To define the law S, input :

user_operator("S",(x,y)->(gcd(x,y))!=1,Binary)

Output :

1

Input :

5 S 7

Do not forget to put spaces around S.
Output :

0

Input :

8 S 12

Do not forget to put spaces around S.
Output :

1