Related Clues:

• River bird to feel remorse
• Subsidiary theorem, in math
• Lexicographer's beginning with novel headword
• Feel sorry to be winger right on the left
• Liberal introducing novel proposition
• Feel sorry about Garbo, briefly
• Theorem offshoot
• Be sorry about white heron on river
• Remorse for something done or left undone
• No pubs in Petersburg - I don't like the sound of that?
• A headword in a dictionary
• Sad to say, no pubs in Petersburg
• Little theorem within a bigger theorem
• The outer of two bracts surrounding each floret in a grass spikelet
• Supporting premise, in logic