6.1.6  Transforming a list into a boolean expression: list2exp

The list2exp command is the inverse of exp2list; it takes lists and tranforms them into boolean expressions. It can do this in two ways.

The first way:

• list2exp takes two arguments:
  • L, a list of values of the form [a₁,…,a_n]
  • x, a variable name.
• list2exp(L,x) returns the boolean expression ((x=a₁) or …(x=a_n)).

Examples.

• Input:
  list2exp([0,1,2],a)
  Output:

  a=0∨ a=1∨ a=2

• Input:
  list2exp(solve(x^2-1=0,x),x)
  Output:

  x=−1∨ x=1

Alternatively:

• list2exp takes two arguments:
  • L, a list where each element of L it itself a list of n values of the form [a₁,…,a_n].
  • vars, a list [x₁,…,x_n] of n variable names.
  In this case:
• list2exp(L,vars) returns a boolean expression of the form ((x₁=a₁) and …and (x_n=a_n) for each list of n values in the first argument, combined with ors.

Example.
Input:

Output: