title: is there a way to check if a function is defined?
body: <p>i'm new in wolfram-mathematica and I wanna know if is there a way to know if a function is already defined. I mean. Is there something like<code>SomeFunction[f[i,j+1]]</code> that returns <code>True</code> or <code>False</code>?</p>
  
  <p>I've been trying with <code>ValueQ</code> function but, it apparently doesn't work for that kind of arguments, <code>j+1</code>.</p>
  
  <p>Thanks in advance.</p>