@mixin myblockquote {
  blockquote {
    @if global-variable-exists(blockquote-color) {
      background: $blockquote-color;
    }
    @else {
      background: lime;
    }

    @if mixin-exists(myblockquote) {
      color: red;
    }
    @else {
      color: blue;
    }

    @if variable-exists(foo) {
      float: left;
    }
    $foo: 1;
    @if variable-exists(foo) {
      float: right;
    }
  }
}

@include myblockquote;