Generator-offset property: Difference between revisions

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We can write sizes of intervals in S as vectors (p, q, r) using the basis (a, b, c).

Suppose for sake of contradiction that P has only one preimage (α, β, γ) in S. Then projecting to S2 shows that S2's generator is the k-step (α + γ)*(a~c) + βb, and Σ2's imperfect generator is located at index n, like Σ1's imperfect generator is. Then S1 and S2 are the same mos pattern (up to knowing which step size is the bigger one) ~~and even the same mode~~. Assume the L of S1 (it could be s, but it doesn’t matter) is the result of identifying b and c, and all instances of s in S1 come from a. Then the steps of S2 corresponding to the L of S1 must be either all b’s or all a~c’s, thus these steps are all b’s in S (otherwise they would be identified with the a, against the assumption that S1 and S2 are the same mos pattern and mode). So S has only two step sizes (a and b), contradicting the assumption that S has exactly three step sizes.

Suppose for sake of contradiction that P has only one preimage (α, β, γ) in S. Then projecting to S2 shows that S2's generator is the k-step (α + γ)*(a~c) + βb, and Σ2's imperfect generator is located at index n, like Σ1's imperfect generator is. Then S1 and S2 are the same mode of the same mos pattern (up to knowing which step size is the bigger one). Assume the L of S1 (it could be s, but it doesn’t matter) is the result of identifying b and c, and all instances of s in S1 come from a. Then the steps of S2 corresponding to the L of S1 must be either all b’s or all a~c’s, thus these steps are all b’s in S (otherwise they would be identified with the a, against the assumption that S1 and S2 are the same mos pattern and mode). So S has only two step sizes (a and b), contradicting the assumption that S has exactly three step sizes.

Only two k-steps of S can project to P in S1, for if P has three preimages (α, β, γ), (α, β’, γ’), (α, β’’, γ’’) in S, then β, β’ and β’’ are three distinct values. Thus these would project to three different k-steps in S3, contradicting the mos property of S3.

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 We can write sizes of intervals in S as vectors (p, q, r) using the basis (a, b, c).
-Suppose for sake of contradiction that P has only one preimage (α, β, γ) in S. Then projecting to S<sub>2</sub> shows that S<sub>2</sub>'s generator is the k-step (α + γ)*(a~c) + βb, and Σ<sub>2</sub>'s imperfect generator is located at index n, like Σ<sub>1</sub>'s imperfect generator is. Then S<sub>1</sub> and S<sub>2</sub> are the same mos pattern (up to knowing which step size is the bigger one) and even the same mode. Assume the L of S<sub>1</sub> (it could be s, but it doesn’t matter) is the result of identifying b and c, and all instances of s in S<sub>1</sub> come from a. Then the steps of S<sub>2</sub> corresponding to the L of S<sub>1</sub> must be either all b’s or all a~c’s, thus these steps are all b’s in S (otherwise they would be identified with the a, against the assumption that S<sub>1</sub> and S<sub>2</sub> are the same mos pattern and mode). So S has only two step sizes (a and b), contradicting the assumption that S has exactly three step sizes.
+Suppose for sake of contradiction that P has only one preimage (α, β, γ) in S. Then projecting to S<sub>2</sub> shows that S<sub>2</sub>'s generator is the k-step (α + γ)*(a~c) + βb, and Σ<sub>2</sub>'s imperfect generator is located at index n, like Σ<sub>1</sub>'s imperfect generator is. Then S<sub>1</sub> and S<sub>2</sub> are the same mode of the same mos pattern (up to knowing which step size is the bigger one). Assume the L of S<sub>1</sub> (it could be s, but it doesn’t matter) is the result of identifying b and c, and all instances of s in S<sub>1</sub> come from a. Then the steps of S<sub>2</sub> corresponding to the L of S<sub>1</sub> must be either all b’s or all a~c’s, thus these steps are all b’s in S (otherwise they would be identified with the a, against the assumption that S<sub>1</sub> and S<sub>2</sub> are the same mos pattern and mode). So S has only two step sizes (a and b), contradicting the assumption that S has exactly three step sizes.
 Only two k-steps of S can project to P in S<sub>1</sub>, for if P has three preimages (α, β, γ), (α, β’, γ’), (α, β’’, γ’’) in S, then β, β’ and β’’ are three distinct values. Thus these would project to three different k-steps in S<sub>3</sub>, contradicting the mos property of S<sub>3</sub>.