Integrity constraint with jointure

Hello,

I would like to add an integrity constraint on one of my tables, but it looks like I need to create a join for that. I would like to have any feed back on how to do it, or why the design is bad, and how to change to a better one...

create table Teams (
 KeyTeam number primary key
);

create table Paths (
 NickName varchar(100) not null,
 KeyTeam references Teams not null,
 Path varchar(500),
 constraint primary key (NickName, KeyTeam)
);

create table Users (
 KeyUser number primary key,
 KeyTeam references Teams not null
);

create table Tasks (
 KeyUser references Users not null,
 NickNameOfPath varchar(100)
);

The Tasks table references the Paths table, but the foreign key is the team of the user, not the user. So I dont know how to define this relation...

Thank you

-- 
Vincent