Well, it's
possible to say it; what lawyers say to each other in the privacy of their own homes is a matter for their own conscience

. Is a contract always between two parties (I'm not a lawyer, and I don't know)? If not, 'bilateral' is problematic (because it assumes that there
are only two parties). Otherwise, your words make sense... although 'manifestation' is a bit odd - I'd use 'agreement' or perhaps 'setting down'; this written agreement sounds rather like a 'memorandum of agreement' - often, in financial circles, abbreviated to 'MOU' (which, for speakers of French, suggests something rather more amicable!

)
b