of real numbers is defined as a if, for all indices , the following inequality holds:
A[i,j]+A[k,l]≤A[i,l]+A[k,j]cap A open bracket i comma j close bracket plus cap A open bracket k comma l close bracket is less than or equal to cap A open bracket i comma l close bracket plus cap A open bracket k comma j close bracket
In the De Stefani curriculum, problems are designed to test five fundamental proof techniques:
Finding a single case where a statement fails to disprove it. 3. Application: The Fibonacci Identity