Figure 2 in the present online version was a copy of Figure 1.
The correct Figure 2 is included below.
![](https://static.cambridge.org/binary/version/id/urn:cambridge.org:id:binary:20221011144944035-0792:S0007114521005213:S0007114521005213_fig1.png?pub-status=live)
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Published online by Cambridge University Press: 26 April 2022
Figure 2 in the present online version was a copy of Figure 1.
The correct Figure 2 is included below.