A writes his name on the back of a bill of exchange. As the effect of this endorsement is to transfer the right to the bill to any person who may become the lawful holder of it, the endorsement is a "valuable security". 31. "A will": The words "a will" denote any testamentary document 32. Words referring to acts include illegal omissions : In every part of this Code, except where contrary intention appears from the context, words which refer to acts done extend also to illegal omission. 33. "Act", "Omission": The word "act" denotes as well a series of acts as a single act; the word "omission" denotes as well a series of omissions as a single omission. 34. Acts done by several persons In furtherance of common intention: When a criminal act is done by several persons, in furtherance of the common intention of all, each such person is liable for that act in the same manner as if it were done by him alone. 35. When such an act is criminal by reason of its being done with a criminal knowledge or intention : Whenever an act, which is criminal only by reason of its being with a criminal knowledge or intention, is done by several persons, each of such persons who joins in the act with such knowledge or intention is liable for the act in the same manner as if the act were done by him alone with the knowledge or intention. 36. Effects caused partly by act and partly by omission: Whoever the causing of a certain effect, or an attempt to cause that effect, by an act or by an omission, is an offence, it is to be understood that the causing of that effect partly by an act and pertly by an omission is the same offence. Illustration A intentionally causes Z's death, partly by illegally omitting to give Z food and partly by beating Z.A has committed murder. 37. Co-operation by doing one of several acts constituting an offence: When an offence is committed by means of several acts, whoever intentionally co-operates in the commission of that offence by doing any one of those acts, either singly or jointly with any other person, commits that offence. Illustrations (a) A and B agree to murder Z by severally and at different times giving him small dose of poison. A and B administer the poison according to the agreement with intent to murder Z. Z dies from the effects of the several doses of poison so administered to him. Here A and B intentionally co-operate in the commission of murder and as each of them dose an act by which the death is caused, they are both guilty of the offence though their acts are separate.