Plus

operand1 + operand2

• If both operands result in numbers, the expression results in the sum of operand1 and operand2.
• If both operands result in sets, the expression results in the set union of operand1 and operand2.
• If both operands result in lists, the expression results in the concatenation of the two lists (a list which consists of all the members of operand1, followed by all the members of operand2).
• If both operands result in strings, the list results in the concatenation of the two strings (a string which consists of all the characters of operand1, followed by all the characters of operand2.)
• Otherwise the expression results in Undefined.

For example:

  5 + 5 = 10
  {5} + {5} = {5}
  [5] + [5] = [5, 5]
  `5' + `5' = `55'