### Introduction

#### Resum

The main aim of this issue, No. 4, is to present several aspects of online mathematics with regard to time. The contributions have been grouped into three blocks: Firstly, time for preparing digital resources and communicating mathematics contents; secondly, the use of time in learning and teaching processes; and thirdly, an analysis of online mathematics over time. In the first group, César Córcoles analyses the relationship between the resources invested in creating learning objects and their effect on students; and Cuartero, Hunter and Pérez set out a solution to reduce the time required to write mathematical formulae in a learning activity. In the second group, the study carried out by Christensen, Gras-Martí and Ávila addresses the question of how much time on average students spend on course-related work, and how this time is distributed; and Sgreccia analyses students' time management in a collaborative task in the context of mathematics teacher training. In the third block, Hettiarachchi and Huertas look at some temporal aspects in e-assessment systems for online mathematics; and Rovira and Sancho explore the relationship between cognitive and affective factors in online mathematics.