class="type-var">'b</span>, <span class="type-var">'v</span>, <span class="type-var">'a</span>)</span> <a href="../Types/index.html#type-below_above">Types.below_above</a></span> <span>&#45;&gt;</span> <span>f_below:<span>(<span class="type-var">'b</span> <span>&#45;&gt;</span> <span class="type-var">'b2</span>)</span></span> <span>&#45;&gt;</span> <span>f:<span>(<span class="type-var">'v</span> <span>&#45;&gt;</span> <span class="type-var">'v2</span>)</span></span> <span>&#45;&gt;</span> <span>f_above:<s