-----Description-----  
This task requires writing a Lean 4 method that determines whether one list is a sublist of another. In other words, the method should check if the first list appears as a contiguous sequence within the second list and return true if it does, and false otherwise.

-----Input-----  
The input consists of two lists of integers:  
sub: A list of integers representing the potential sublist.  
main: A list of integers in which to search for the sublist.

-----Output-----  
The output is a Boolean value:  
Returns true if the first list appears as a contiguous sequence within the second list.  
Returns false if the first list does not appear as a contiguous sequence in the second list.

-----Note-----  
There are no preconditions for this method; the sequences are always non-null.