Cognidia requires a Reason for each step in the solution. The Reason justifies how a step transforms to the next step. The Reason should be specific and apply to the expression in the first step directly without assuming any other transformation. For example, eval justifies evaluation of independent arithmetic operations. In this problem, eval is used to justify 2 * 5 = 10 and 2 * 2 = 4

The Cognidia Reference page - https://cognidia.com/reference - provides the list of all available Reasons and their definitions.