6.12.17  Substituting a variable by a value: |

The | operator is an infixed operator that evaluates an expression after giving values to some variables. It does not evaluate the expression before the variables are replaced by the requested values.

• | is an infixed operator, so takes two arguments:
  • expr, an expression depending on one or more variables on the left hand side.
  • x₁=a₁, ldots; an equality or sequence of several equalities.
• expr|x₁=a₁,… returns the expression expr with x₁ replaced by a₁, etc.

Examples.

• Input:
  a^2 + 1 | a = 2
  Output (even if a has been assigned a value):

  5

• Input:
  a^2 + b | a = 2, b = 3
  Output (even if a or b had been assigned a value):

  7