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In the workbook that I'm working with, there is a strange structure of sentence for me and I would like to check with you if it's not wrong or mistake such as typo. The sentence is:
Only after buying the cottage did we discover that it was infested with mice"
We can use also the auxiliary verb as an emphasizer but in such cases it should come after the verb (e.g. Only after buying the cottage we did discovered that it was infested with mice"). In addition, I do not understand the omission of the past form (ed) from the word "discover".