Is it possible to create a local/private sass mixin?

I have three sass files: a.scss, b.scss, c.scss

a.scss:

@mixin font($size, $color){
  font-size: #{$size};
  color: #{$color}
  }

 p{
  @include font(10px, blue)
  }

b.scss:

@mixin font()
{
..
}

c.scss

@import a.scss
@import b.scss

I think the mixin font() in b.scss override the mixin font($size, $color) in a.scss.

p{
  @include font(10px, blue)  // use mixin font() in b.scss, error
  }

Is it possible to create a local/private sass mixin? Or all mixins in sass are global, I have to give them unique name for each mixin?