This is an interesting, though not necessarily a common proposition. Generally, the dilution occurs equally, i.e., both the founders undergo dilution equally. However, dilution is purely a matter of contract and nothing prevents one founder from diluting his shareholding or having the other founder dilute his shareholding. Conceptually, if the shares are being transferred from the founder to the investor, then this is a process of share transfer, as opposed to a share issuance by the Company where, by default, the dilution will be equal. Even then, one founder may be granted such additional shares during the process of share issuance, so as to arrive at the intended shareholding structure that you mentioned. However, you should take care of appropriate documentations such as the investment agreement, term sheet, founder's agreement, share transfer agreement, etc. in order to achieve your desired result.
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