Problem 1
Begin from the exact definitions, verify all hypotheses, use second countable ⇒ separable, distinguish local from global conclusions, and test the result on a standard model and a boundary or counterexample case.
Faculty solution guide
Second Countability, Separability and Lindelöf Ideas
Accept equivalent mathematically correct reasoning. Require explicit definitions, theorem hypotheses, proof structure, verification, and limitations.
Problem 2
Identify the first invalid inference, missing hypothesis, quantifier error, unjustified limit interchange, or unproved existence claim; then supply a valid repair.
Problem 3
A complete response explicitly states the definitions, domain, hypotheses, exact target, and theorem dependencies for Second Countability, Separability and Lindelöf Ideas.
Problem 4
The argument must address relating global countable bases, dense sets, and countable subcovers with each nontrivial step justified and the final conclusion restated.
Problem 5
A strong application explains the mathematical model in analysis, optimization, computational geometry, function spaces, and scientific models, verifies conditions, and names at least one limitation.
Problem 6
Accept a second valid proof, a counterexample showing necessity of a hypothesis, an independent estimate, or a reproducible finite check that is correctly described as supporting evidence.