Using a dictionary in Xojo

How do I check a dictionary to see if a number has previously been returned for parameters i and j of an array of Size x Size? This is what I have so far:

Dim settings As New Dictionary // instantiate the Dictionary
For i=0 to Size-1
    For j=0 to Size-1
      if // check in dictionary if a number has been previously returned for the i,j parameters
        Return // number
       else
...

lookup or HasKey