## `Type::Relation` -- type for testing relations

#### Introduction

With `Type::Relation`, relational expression can be identified.

#### Call(s)

`testtype(obj,` Type::Relation)

#### Parameters

`obj` | - | any MuPAD object

#### Returns

see `testtype`

#### Related Functions

`testtype`

#### Details

- The call `testtype(obj,` Type::Relation) checks, whether `obj` is a relational expression and returns `TRUE`, if it is, otherwise `FALSE`.
- A relation in MuPAD is an expression of the type `"`_equal", `"`_unequal", `"`_less" and `"`_leequal".

  Expressions with the operations `>=` and `>` will be interpreted as expressions with `<=` and `<` by exchanging the operands (see example 2).

- This type does not represent a property.

#### Example 1

`x > 3` is a relation, while `TRUE` is not:

    >> testtype(x > 3, Type::Relation),
       testtype(TRUE, Type::Relation)

                                    TRUE, FALSE

#### Example 2

MuPAD always interprets expressions with the operations `>=` and `>` as expressions with `<=` and `<` with the operands exchanged:

    >> x > 3;
       prog::exprtree(x > 3):

                                       3 < x

                                       _less
                                       |
                                       +-- 3
                                       |
                                       `-- x

The operator is not `>`, but `<`, and the operands have been swapped:

    >> op(x > 3, 0..2)

                                    _less, 3, x

#### Changes

- no changes

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