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## `SFA::SfAVars` -- specifies valid variables in alphabets

#### Call(s)

`SFA::SfAVars(vset)`

#### Parameters

`vset` | - | a set of variables

#### Introduction

The `SFA::SfAVars` function specifies which variables are considered for the `SfAExpand` function.

`vset` gives the set of valid variables for `SFA`, for instance:

- `{x1, x2, x3 }`
- `{{x}, {y}}`, all the `x`i's and `y`i's,
- `{{x}, {y}, t }` all the `x`i's and `y`i's, and the variable `t`.

With no argument, `SFA::SfAVars` returns the current set of valid variables.

Note that each call to `SFA::SfAVars` destroy the remember table of `SfAExpand`, if `vset` is specified.

#### Example 1

    >> muEC::SFA::SfAVars( {{x}, u, v} );

                                    {{x}, u, v}

    >> tt := muEC::SFA::SfAExpand( m[3,2](x1+u+v) - q*s[2,2](x1+u+v) );

           2  3    3  2    2   3    3   2    2   3    3   2      2  2
          u  v  + u  v  + u  x1  + u  x1  + v  x1  + v  x1  - q u  v  -

                2   2      2   2           2        2         2
             q u  x1  - q v  x1  - q u v x1  - q u v  x1 - q u  v x1

#### Related Functions

`SfAExpand`

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MuPAD Combinat, an open source algebraic combinatorics package