Define an operator: user_operator

### 2.14.3 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 annulate 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 by 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`