1. Infeasibility:

• Definition: No feasible solution exists that satisfies all constraints simultaneously. The feasible region is empty.  
• Effect on Solution Process: The simplex method will eventually indicate infeasibility. Graphically, the constraint lines do not intersect to form a common feasible region.
• Operations Research Impact: Indicates a problem with the model formulation. Constraints may be too restrictive, or there might be an error in the data. Requires re-evaluation and modification of the constraints.  

2. Unboundedness:

• Definition: The feasible region extends infinitely in at least one direction, and the objective function can increase (maximization) or decrease (minimization) without limit.  
• Effect on Solution Process: The simplex method will detect unboundedness. Graphically, the feasible region is open, and the objective function line can be moved indefinitely in a direction that improves the objective value.  
• Operations Research Impact: Suggests an issue with the model. Constraints may be missing, or they might not be properly formulated. Requires re-examination of the model to add appropriate constraints and bound the feasible region.

3. Degeneracy:

• Definition: Occurs when one or more basic variables in the simplex tableau have a value of zero. This can lead to stalling (cycling) in the simplex method.
• Effect on Solution Process: The simplex method might take more iterations than usual or, in rare cases, get stuck in a loop (cycling) and never reach the optimal solution.
• Operations Research Impact: While degeneracy doesn't prevent finding the optimal solution in most cases, it can make the process less efficient. Special techniques (like Bland's rule) can be used to prevent cycling.  

4. Multiple/Alternate Optimal Solutions:

• Definition: More than one combination of decision variable values leads to the same optimal objective function value.
• Effect on Solution Process: The simplex method will identify one optimal solution. If alternate optima exist, they can sometimes be found by further analysis of the final tableau. Graphically, the objective function line is parallel to a binding constraint.
• Operations Research Impact: Provides flexibility in decision-making. The decision-maker can choose among the alternate optimal solutions based on other criteria not explicitly included in the model.

5. Redundancy:

• Definition: A constraint that, if removed, would not change the feasible region. It's "covered" by other constraints.  
• Effect on Solution Process: Redundant constraints don't affect the optimal solution, but they can make the problem larger and computationally less efficient.  
• Operations Research Impact: Identifying and removing redundant constraints simplifies the problem without changing the optimal solution.  

6. Non-Linearity (Not strictly a "special case," but a deviation from standard LP):

• Definition: The objective function or constraints are not linear.
• Effect on Solution Process: The simplex method cannot be used.
• Operations Research Impact: Requires different optimization techniques (e.g., non-linear programming algorithms) to solve the problem.