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Errors: The system is divided into two primary steps, creating the order and placing the order. In each of these steps the user is able to back up and reverse any of the choices they have made, but they can't usually jump between states. This is alleviated by making the most important details (e.g. participants, restaurant selections) modifiable by all users in the second stage. For example, sharing the link to the page allows one user to add additional people to the order, even after the ordering has begun. The second page only allows adding (and not removing), though, as it ensures that the involved parties will never lose track of what happened in the past and lead to their current state.
Design 3: 
one.
Julian wants to make an order with his friends. he goes to the site and sees the three steps he needs to take to do so.
He picks his restaurant of choice from a drop down list
He searches for groups of friends and select them in groups
He decides that he only wants people to be contacted by email, so unchecks phone and IM.
Everything seems okay to him, so he clicks GO!
two.
Karen is invited to the group via email and clicks on the link she gets.
She is presented with a page with a menu on the left and looks through the choices, gets some rice...
Looks over to what other people are getting...lamb curry! She loves lamb curry, how cold she have forgotten to get that!
Karen adds lamb curry and sees that her total comes out to be $13.52. She clicks Done Ordering at the bottom of the page and waits.
three.
The order is in and Julian sees everyone who is in the order and what they individually need to pay. The others do neo see this.
When people approach him and ask him what they owe, he clicks on their face and tells them.
When they pay, he clicks the paid button unter the price.
four.
Karen gets an email teller to pay Julian 13.52.
She goes over to him, gives him the money, and he checks her off on the above page.
She returns to her computer and sees that she has been marked as paid!
General Comments on Design 2
First page visibility/efficiency questionable.