grammar - Is usage of word "some" has the same meaning as indefinite article?

Is that true that the indefinite article can be always replaced with word "some" and it will be nearly always the same meaning?

Examples:

I have bought a house = I have bought some house

I walked in the forest and have met a squirrel = I walked in the forest and have met some squirrel

The sandwich contains a cheese = The sandwich contains some cheese

Am I correct?

Answer

Yes, that's correct - or at least I can't think of a way it's not. The "some" you are referring to is the some that is used to define some unspecified or unknown thing. It is not the quantitative use of the word. It sounds a little dorky sometimes, but it definitely works.

It even works in this wack sentence because of how lot can be defined: I don't like a lot of people - I don't like some lot of people

Your second example is a bit odd. It should read more like: "I walked in the forest and met a/some squirrel." This is not dependent on changing "a" to "some", it just doesn't make sense grammatically to use it that way because the first action of walking is in the past tense whereas the second action of meeting the squirrel is in present tense. It could also be "I met a squirrel when I walked in the forest", or "While walking in the forest I met a squirrel".